Vacuum servo advance mechanism



Feb. 28, 1967 BEVACQUA 3,306,272

VACUUM SERVO ADVANCE MECHANISM Filed April 1, 1965 2 Sheets-Sheet ladvance FIG. I

, INVEM'OI' LOUIS A. BEVACQUA Feb. 28, 1967 A, BEVAC UA 3,306,272

VACUUM SERVO ADVANCE MECHANISM Filed April 1, 1965 2 Sheets-Sheet 2 FIG.

FLYWHEEL DEGREES VACUUM IN INCHES hg.

\h Invenror l9 l4 By LOUIS A. BEVACQU-A United States Patent 3,306,272VACUUM SERVO ADVANCE MECHANISM Louis A. Bevacqua, Des Plaines, Ill.,assignor to Motorola, Inc., Franklin Park, Ill., a corporation ofIllinois Filed Apr. 1, 1965, Ser. No. 444,760 8 Claims. (Cl. 123-117)This invention pertains generally to a vacuum servo ad vance mechanism,and more particularly to a vacuum servo mechanism for the ignition timerof an automobile engine which both advances and retards the timer atdiiferent engine speeds.

Reduction of smog in large cities has become an increasingly importantproblem. To meet this problem it is highly desirable that automobileengines be designed to operate so that the hydrocarbons which areemitted in the exhaust from the engines are substantially reduced. Oneway to reduce this emission of hydrocarbons in the exhaust is byretarding the engine ignition timing during the time that the car isidling, for instance, when stopped in heavy trafiic or at a trafliclight.

Present ignition timers have the spark advance set at the manufacturersrecommended position for starting, and then advance the spark withincreased engine r.p.m. Therefore, the engine ignition timing is thesame during idling as at starting, or slightly advanced with respect tothe starting position. To retard the timing further at starting wouldpresent the problem of hard starting, loss of power, and overheating athigh rpm.

It is, therefore, an object of this invention to provide an improvedvacuum servo advance mechanism for an automobile ignition timer.

It is another object of this invention to provide a vacuum servomechanism for an engine ignition timer that permits starting anautomobile engine at the optimum timing, retarding the ignition timingbelow the position for starting while idling, and then advancing theengine timing with increased engine vacuum.

A feature of this invention is the provision of a vacuum servo mechanismhaving one vacuum actuated diaphragm coupled through a mechanicallinkage to provide mechanical motion in two directions.

Another feature of this invention is the provision of a vacuum servoadvance mechanism having a first fixed plate, a second plate rotatablymounted with respect to the first plate, and a third plate pivotallymounted to the first fixed plate and supporting a servo body including avacuum actuated diaphragm. The diaphragm is connected through amechanical linkage to the second plate and moves the same first in onedirection relative to the first plate, and upon increased vacuum in theservo body moves the second plate relative to the first plate in thedirection opposite to the one direction.

In the drawings:

FIG. 1 is a plan view of the vacuum servo mechanism for an ignitiontimer with the position for engine idling shown in dotted lines;

FIG. 2 is a bottom view FIG. 1;

' FIG. 3 is a plan view of the same mechanism showing the engine runningat an rpm. greater than at idling;

FIG. 4 is a side view of the mechanism; and

FIG. 5 is a graph illustrating the operation of the mechanism of theinvention.

In accordance with this invention, a vacuum servo mechanism for anignition timer is provided having a first fixed plate, a second platerotatably mounted with respect to the first plate, and a third platepivotally mounted to the first plate, and which supports a servo bodyhaving a vacuum actuated diaphragm. A first rod is connected from thediaphragm to the second plate by means of a right angle portion thatextends through an arcuate of the same mechanism of 3,306,272 PatentedFeb. 28, 1967 slot in the first plate. A first spring connects the rightangle extension to the fixed plate and biases the extension fromslidably engaging the second plate. A second rod is connected betweenthe second and third plates through a second spring.

Initial vacuum in the servo body actuates the diaphragm which attemps todraw the first rod connected to the diaphragm toward the vacuum side ofthe diaphragm. However, the tension of the first spring connecting theextension of the rod to the first plate is sufi'iciently great that therod remains stationary and the servo body is drawn towards thediaphragm. As the servo body pivots about the fixed plate, the motion istranslated through the second rod to move the second plate in aretarding direction relative to the first plate. As the vacuum in theservo body is increased, the pressure diiferential is great enough forthe diaphragm to overcome the first spring tension, so that theextension of the first rod engages the second plate and draws the sameagainst the bias of the first and second springs to move the secondplate relative to the first plate in the opposite or advance direction.

The device of the invention is described for use as a vacuum servoadvance mechanism for an automobile ignition timer. It should beunderstood that this device may find utility in other applications wherea vacuum servo advance mechanism is desirable.

In FIGS. 1 through 4, a first fixed plate 10 is mounted to housing 11 byscrews 12 and 13. A drive shaft 14 extends coaxially and rotatablywithin the housing 11. A cam 15 on the drive shaft 14 has a shoulder 17which is in rotatable contact with bearing surface or bush 19. As thedrive shaft 14 turns inside the housing 11, the cam 15 is turned tooperate the ignition timing points 20 in the known manner. A second orbreaker plate 22 has an aperture 24 through which bush 19 passes. Theplate 22 is rotatably and coaxially mounted with respect to plate 10 andhousing 11, and carries the ignition timing points 20 which can bestatically adjusted on the plate 22 by screw 90.

A vacuum servo body 25 is connected to a third plate 26. This thirdplate 26 is pivotally mounted to the first fixed plate 10 by pivot post28 passing through the bracket 29 and secured by crescent lock washer30. The servo body 25 has an inlet 32 connected to the vacuum line (notshown) extending from the engine intake manifold as is well known tothose familiar with the art. The vacuum in the servo body, therefore,varies in the same sense as the crankshaft rpm. of the engine. A spring34 (FIG. 2) is inserted between the diaphragm 35 and the wall 36 of theservo body 25. The spring 34 biases the diaphragm 35 to oppose movementof the diaphragm 35 towards the vacuum side 60 of the servo 25. Thisspring 34 regulates the advance of the mechanism as will be described.

A first rod 37 has one end thereof connected through an aperture in theservo body 25 to the face of the dia phragm 35 at 38. A second end has aright angle extension 40 connected to it by coupling 43. The right angleextension 40 extends through an arcuate slot 42, and a spring 44connects the extension 40 to a projection 46 on the first fixed plate22. A second rod 48 has one end, a right angle extension 50, that isinserted through an aperture in plate 26 and secured to that plate bycrescent lock washer 51. The second end 53 is inserted through anaperture in a tab 52, that was cut from plate 22 and bent into position.A crescent lock washer 55 prevents the end 53 from slipping out of thetab 52. A spring 56 encircles the rod 48 and has one end butted againstthe tab 52 and the other end butted against shoulder 58 that is pinchedto the rod 48.

The full lines in FIGS. 1 and 2 indicate the position of the device withthe engine stopped. At this point the timing is set at the manufacturersrecommended position for starting. After the engine has started andbegins to idle, the components are rotated as indicated in the dottedlines to retard the spark. When the engine is idling, for example,between 300 to 600 r.p.m., the vacuum side 60 of the servo 25 issubjected to a pressure of approximately two inches of mercury. Theother side 61 of the servo is open to atmospheric pressure, so that whenthe vacuum is drawn the diaphragm 35 tends to move toward the vacuumside 60 in an attempt to equalize the pressure. This motion is resistedby spring 34. The pressure of the spring 34 is reduced somewhat from thestandard diaphragm return spring generally used in the art, in order topermit motion of the diaphragm at a lower than normal vacuum. As thediaphragm 35 moves, it attempts to carry rod 37 with it, however, thetension of spring 44 is greater than the pressure differential at idlingspeeds, with the result that the entire servo body 25 rather than thediaphragm 35 moves about pivot 28 to equalize the pressure. This motionof the servo body 25 connected to plate 26 is transmitted through rod 48and tab 52 to move breaker plate 22 clockwise. This clockwise movementof the plate 22 moves the points 20, which are mounted on the plate 22,in a similar fashion to retard the spark, for example, as shown by thedotted line 20'. The rotation of the body 25 about pivot post 28 islimited by stop 62 meeting plate 10, as shown by dotted line 62 and thesimultaneous meeting of plate 22 with extension 40, as shown by thedotted and dashed line 22'.

When the engine r.p.m. is increased above idling, the vacuum increasesthereby increasing the pressure differential on either side of thediaphragm 38. When this pressure differential is great enough toovercome the tension of spring 44, spring 56 and spring 34, thediaphragm 35 will move toward the vacuum side 60 of the body 25 and drawrod 37 with it. This motion of rod 37 causes extension 40, which hadbeen biased by spring 44 from slidably engaging plate 22, to slide inarcuate slot 42. Since extension 40 was in contact with plate 22 at 22'(FIG. 1), as previously stated, this sliding action of the extension 40will move the breaker plate 22, hence points 20, in a counter clockwisefashion to advance the spark.

FIG. 3 shows the points advanced with the engine running at some r.p.m.greater than at idle. Dotted lines show the relative position of thebreaker plate 22, at starting 64 and in the retarded position whileidling 65. The advance position 66 is shown in solid.

It should be noted that once the vacuum gets to approximately two inchesof mercury the servo body 25 will rotate until the stop 62 hits thefixed plate 10 and will remain in this position, even when the breakerplate 22 is advanced, until the vacuum decreases below approximately twoinches of mercury. In addition, the combined tension of springs 44, 56and 38 is substantially equal to the normal tension of a standarddiaphragm return spring commonly used in the art. This insures that thetiming will be advanced when the engine r.p.m. is increased above idlingspeeds in accordance with the manufacturers recommendations.

The operation of this invention may be better understood by referring tothe graph of FIG. 5. The change in flywheel degrees is plotted againstthe change in vacuum in inches of mercury, with the dotted line 70indicating the standard advance recommended by the manufacturer, and thesolid line 72 indicating the advance and retarding action of thestructure of this invention.

Using a standard ignition advance mechanism, the engine of the vehicleis started with the advance as indicated at 75 and remains at therecommended starting position during the entire idling range, or untilthe vacuum is about five inches, as indicated at 76. At this point thetiming is advanced by the increased vacuum in the same sense as theengine r.p.m., along the line 78.

With the vacuum servo mechanism of this invention, however, the vehicleis started at the manufacturers recommended position for starting 75,but as the vacuum increases to about two inches during idling, theignition timing is retarded 10 in the manner previously described and asshown at on the graph. The curve between points 80 and 82 is relativelyfiat representing the period where the vacuum is increased from theidling range but is still not great enough to overcome the tension ofspring 34 to advance the timing. However, because the tension of spring34 is reduced from that of the standard spring, a slight increase invacuum (point 82) from the idling range causes the ignition timing to berapidly advanced. This is shown by line 72 which continues to riserapidly until the combined tensions of spring 44, spring 56 and spring34 cooperate to regulate the timing advance. At the point 85, the twocurves merge, and the timing is advanced from that point in accordanceWit-h the manufacturers recommendation.

It is possible during heavy engine loads and deceleration to eliminatethe retarding of the timing. This could be done by reducing the vacuumbelow one inch during the periods that the elimination of the retardingof the timing was desired thereby permitting the servo body to return toits stop position. Vacuum could be reduced by throttle settings, relaysand other known methods.

What has been described, therefore, is an improved vacuum servo advancemechanism which uses only one diaphragm to provide mechanical motion intwo directions. This makes it possible to start an engine at themanufacturers recommended timing, then retard the ignition timing belowthat of the manufacturers recommended position while idling, and thenadvance the engine timing with the increased engine vacuum in accordancewit-h the manufacturers recommendations.

What is claimed is:

1. A vacuum servo advance mechanism including in combination, a firstfixed plate, a second plate rotatably mounted with respect to said firstplate, vacuum means to rotate said second plate relative to said firstplate including a vacuum actuated diaphragm, pivotal means supportingsaid vacuum means on said first plate and linking means coupling saiddiaphragm and said pivotal means to said second plate, said diaphragmbeing responsive to an initial vacuum and acting through said linkingmeans to move said second plate in one direction relative to said firstplate, said linking means being responsive to increased movement of saiddiaphragm to move said second plate relative to said first plate in adirection opposite to said one direction.

2. A vacuum servo advance mechanism for use with an automobile engineignition timer and for actuation by vacuum taken from the automobileengine which varies in the same sense as the engine r.p.m., thecombination including a first fixed plate, a breaker plate rotatablymounted with respect to said first plate, vacuum means to rotate saidbreaker plate relative to said first plate to advance and retard theengine ignition timing including a vacuum actuated diaphragm, pivotalmeans supporting said vacuum means on said first plate and linking meanscoupling said diaphragm and said pivotal means to said breaker plate,said diaphragm being responsive to the vacuum taken from the engine atidling r.p.m. and acting through said linking means to move said breakerplate in one direction relative to said first plate to retard theignition timing, said linking means being responsive to increasedmovement of said diaphragm with increased engine r.p.m. above saididling r.p.m. to move said breaker plate relative to said first plate inthe direction opposite to said one direction to advance the ignitiontiming.

3. A vacuum servo advance mechanism including in combination, a firstfixed plate, a second plate rotatably mounted with respect to said firstplate, a third plate pivotally mounted to said first fixed plate, vacuummeans. to rotate said second plate relative to said first plateincluding a servo body having a vacuum actuated diaphragm, said servobody being mounted to said third plate, linking means coupling saiddiaphragm and said third plate to said second plate, and spring meanscoupled between said first plate and said diaphragm, said linking meansbeing responsive to initial vacuum applied to said diaphragm for movingsaid second plate in one direction relative to said first plate, saidlinking means being responsive to increased vacuum for moving saidsecond plate relative to said first plate in a direction opposite tosaid one direction, with said spring means preventing said motion insaid direction opposite to said one direction until the limit of saidmotion in said one direction is reached.

4. A vacuum servo advance mechanism including in combination, a firstfixed plate having an arcuate slot therein, a second plate rotatablymounted with respect to said first plate, servo means including a vacuumactuated diaphragm, pivotal means supporting said servo means on saidfirst fixed plate, linking means including a firs-t rod coupled to saiddiaphragm and slidably engageable with said second plate and a secondrod coupled between said pivotal means and said second plate, withinitial vacuum in said servo means actuating said diaphragm to causesaid pivotal means to pivot with respect to said first plate therebycausing said second rod to move said second plate in one directionrelative to said first plate, and increased vacuum in said servo meanscausing said diaphragm to move said first rod thereby moving said secondplate relative to said first plate in a direction opposite to said onedirection.

5. A vacuum servo advance mechanism for an engine ignition timer,including in combination, a first fixed plate, a second plate rotatablymounted with respect to said first plate, a third plate pivotallymounted to said first fixed plate, a servo body including a vacuumactuated diagram fixedly mounted to said third plate, linking meansincluding a first rod coupled to said diaphragm and slidably engageablewith said second plate and a second rod coupled between said third plateand said second plate, and spring means coupled between said first rodand said first fixed plate, with initial vacuum in said servo bodyactuating said diaphragm whereupon said diaphragm and said spring meanscooperate causing said third plate to pivot with respect to said firstplate thereby causing said second rod to move said second plate in onedirection relative to said first plate, and increased vacuum in saidservo body causing said diaphragm to move said first rod thereby movingsaid second plate relative to said first plate in the direction oppositeto said one direction.

6. A vacuum servo advance mechanism for an engine ignition timerincluding in combination, a first fixed plate having an arcuate slottherein, a second plate rotatably mounted with respect to said firstplate, a third plate pivotally mounted to said first fixed plate, aservo body having a vacuum actuated diaphragmfixedly mounted to saidthird plate, a first rod having one end connected to said diaphragm anda second end having a right angle extension slidably extending throughsaid arcuate slot and engageable with said second plate, a first springconnecting said right angle extension to said fixed plate and biasingsaid extension from slidably engaging said second plate, a second rodhaving one end connected to said third plate and a second end, a secondspring connecting said second end of said second rod to said secondplate, with initial vacuum in said servo body actuating said diaphragmto cause said third plate to plvot with respect to said first platethereby causing said second rod to move said second plate in onedirection relative to said first plate, and increased vacuum in saidservo body causing said diaphragm to move said firs-t rod therebysliding said right angle extension in said arcuate slot into engagementwith said second plate and moving the same against the bias of saidfirst and second springs relative to said first plate in the directionopposite to said one direction.

7. A vacuum servo advance mechanism having a servo body with a springreturn diaphragm for an engine ignition timer, the combination includinga first fixed plate having an arcuate slot therein, a breaker platerotatably mounted with respect to said first plate, a third plate withthe servo body being fixedly mounted thereto, said third plate beingpivotally mounted to said first fixed plate, a first rod having one endconnected to the diaphragm and a second end having a right angleextension slidably extending through said arcuate slot and engageablewith said breaker plate, a first spring connecting said right angleextension to said fixed plate and biasing said extension from slidablyengaging said breaker plate, a second rod having one end connected tosaid third plate and a second end, a second spring connecting saidsecond end of said second rod to said breaker plate, with initial vacuumin the servo body actuating the diaphragm to cause said third plate topivot with respect to said first plate thereby causing said second rodto move said breaker plate in one direction relative to said firstplate, and increased vacuum in the servo body causing said diaphragm tomove said first rod thereby sliding said right angle extension in saidarcuate slot into engagement with said breaker plate and moving the sameagainst the bias of said first and second springs and the diaphragmreturn spring relative to said first plate in the direction opposite tosaid one direction.

'8. A vacuum servo advance mechanism for use with an automobile engineignition timer and for actuation by vacuum taken from the automobileengine which varies in the same sense as the engine r.p.m., thecombination including a first fixed plate having an arcuate slottherein, a breaker plate rotatably mounted with respect to said firstplate, a third plate pivotally mounted to said first fixed plate, aservo body having a vacuum actuated diaphragm fixedly mounted to saidthird plate, a first rod having one end connected to said diaphragm anda second end having a right angle extension slidably extending throughsaid arcuate slot and engageable with said breaker plate, a first springconnecting said right angle extension to said fixed plate and biasingsaid extension from slidably engaging said breaker plate, a second rodhaving one end connected to said third plate and a second end, a secondspring connecting said second end of said second rod to said breakerplate, with initial vacuum in said servo body taken from the engine atidling r.p.m. actuating said diaphragm to cause said third plate topivot with respect to said first plate thereby causing said second rodto move said breaker plate in one direction relative to said first plateto retard the ignition timing and increased vacuum in said servo bodytaken from the engine at some r.p.m. greater than said idling r.p.m.,causing said diaphragm to move with said first rod thereby sliding saidright angle extension in said arcuate slot into engagement with saidbreaker plate and moving the same against the bias of said first andsecond springs relative to said first plate in the direction opposite tosaid one direction to advance the ignition timing.

References Cited by the Examiner UNITED STATES PATENTS 3,162,184 12/1964Walker 12.3117 3,220,395 11/1965 Julian 123-14-6.5

MARK NEWMAN, Primary Examiner.

R. D. BLAKESLEE, Assistant Examiner.

1. A VACUUM SERVO ADVANCE MECHANISM INCLUDING IN COMBINATION, A FIRSTFIXED PLATE, A SECOND PLATE ROTATABLY MOUNTED WITH RESPECT TO SAID FIRSTPLATE, VACUUM MEANS TO ROTATE SAID SECOND PLATE RELATIVE TO SAID FIRSTPLATE INCLUDING A VACUUM ACTUATED DIAPHRAGM, PIVOTAL MEANS SUPPORTINGSAID VACUUM MEANS ON SAID FIRST PLATE AND LINKING MEANS COUPLING SAIDDIAPHRAGM AND SAID PIVOTAL MEANS TO SAID SECOND PLATE, SAID DIAPHRAGMBEING RESPONSIVE TO AN INITIAL VACUUM AND ACTING THROUGH SAID LINKINGMEANS TO MOVE SAID SECOND PLATE IN ONE DIRECTION RELATIVE TO SAID FIRSTPLATE, SAID LINKING MEANS BEING RESPONSIVE TO INCREASED MOVEMENT OF SAIDDIAPHRAGM TO MOVE SAID SECOND PLATE RELATIVE TO SAID FIRST PLATE IN ADIRECTION OPPOSITE TO SAID ONE DIRECTION.